The invention relates to tubes and containers for transport and storage of petrol and hydrocarbons of a type similar to petrol, typically for use in petrol station installations and other similar installations where petrol or. other hydrocarbons as i.a. kerosene, diesel oil, fuel oil, natural gas, LPG, or the likeare stored in tanks and from there supplied to e.g. the pumps in the filling station. Among the areas of usage for these tubes the following may be mentioned, pipes for venting and return of gases and other distributional areas.
In installations of the type referred to above it has been common to use galvanized tubes each having a length of 6 meters, which means that the tubes have to be joined together. A joint always represents a threat of leakage. This threat is heightened by the fact, that the weather changes during the seasons of the year, gives effects from movements in the ground which effects cannot be entirely avoided. It must of course be pointed out that even if the tubes are laid in the form of a continous hose of a plastic material, suitable for the application, the forces from the ground. movements remain, but on account of the inherent properties of the material the results of the existing forces may be. essentially eliminated. However the risk for leakage of hydrocarbons by diffusion remains.
The leakage from the tubes generally used for this purpose may approximately be estimated to 0.4 g/meter and month, i.e. 2,5 1/meter and year. This estimate refers to polyethene tubes of the usual types. In addition to polyethene tubes, also tubes of glass fiber reinforced plastic material is used.
The object of the invention is thus tubes or containers for transport and/or storing of petrol or hydrocarbons having similar properties, tubes manufactured from a material, said material being chemically compatible with said hydrocarbons and said material a reduced absorption as to transported or stored hydrocarbons. Moreover the tubes are diffussion resistant to such an extent that they may be installed in the ground with a higher degree of safety than the tubes existing up to now.
Generally speaking, most polyolefines may be used for transporting petrol bearing in mind that most of the polyolefines show resistance towards petrol to a greater or smaller extent. Among these are polyethene and polypropylene, which materials are chemically inert and which also show favourable properties when used in connection with hydrocarbons. The most common use in this context is fuel tanks for installation in cars, said tanks for more than ten years having been manufactured from polyethene.
However, the matrix of polyethene (i.e. the molecular network of the material) does not belong to the most diffusion resistant plastics, since through this material diffuses and in the material is absorbed certain amounts of solvents e.g. petrol. The thickness of the manufactured goods is of essential importance as are the sorrounding weather conditions, especially the temperature if the tube is installed above ground and if the tube is installed in the ground the effective factors are essentially the same. That different types of plastics show different permeability factors is well know in the art and this fact is used in various applications.
It is know in other fields of usage to coat tubes on the outside to hinder diffusion from the outside of gaseous elements or compounds into the tube, conf. e.g. the coating on the outside of water-pipes in order to hinder the admittance of oxygen to the circulating hot water in the radiator circuits.
It is also known to seal the inside of the fuel tanks in cars by laquering them in order to stop the petrol fumes from diffusing. This type of treatment can-for natural reasons not be applied to continous tubes.
A gaseous diffusion resistant article is know from EP,A,2,0030091 comprising 3 layers, of which one is the intermediate layer so chosen as to be an adhesive for both the layers and such that said layer also compensates for the relative coefficients of linear expansion between the, intermediate layer and its adjoining layers. These tubes may be formed by co-extrusion. This tube is meant for central heating systems and they thus have to be able to stand for a vide variety of temperatures, much wider than the temperature range for the tubes according to the invention.
A number of documents showing examples of prior art in the relevant field are the following JP,A,2035290, JP,A,3197034, JP,A,3224735.